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I'm trying to convert the frequency of a 0-5V square wave, which ranges from 0-20kHz, to a voltage using a simple LM2907 (8 pin) circuit.

Using R1 as 100k, I've calculated C1 to be 416pF for a maximum output of 12V @ 20kHz.

However, when I do a transient simulation, all I get is an exponentially shrinking output voltage starting at ~2mV.

What simulation settings should I use in LTSpice to verify the linearity of my frequency-to-voltage converter? Transient, DC operating point? Some kind of sweep?

Here is my circuit: alt text http://img840.imageshack.us/img840/6758/lm2907ftovtest.png

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  • \$\begingroup\$ Still no luck on my end. Ideas, anyone? \$\endgroup\$ – Petrus Theron Sep 14 '10 at 10:25
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A time domain transient sweep is what you would use in OrCAD PSpice - LTSpice should have something similar. A DC bias point analysis is of no help with a dynamic signal (pulsed source). An AC analysis is for things like gain and phase analysis of filters.

If the results look a little funky, see if there's an option to skip the initial bias point calculation - it may cause the simulation to take longer but you often get better (i.e. more realistic) results when dealing with dynamic circuitry.

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